Bruins enforcer Shawn Thornton will appeal the 15-game suspension handed down by the NHL’s Department of Player Safety, a result of Thornton’s attack on Brooks Orpik in a game against the Penguins Dec. 7. Thornton filed a written appeal on Monday, after having a 48-hour window to let the NHL know of his decision. That window was set to expire at 4 p.m. on Monday.

The Players’ Association tweeted, “Shawn Thornton has decided to appeal the League’s decision to suspend him for 15 games, and on his behalf the NHLPA has notified the NHL.”

The 15-game suspension was the longest that senior vice president of player safety Brendan Shanahan has handed down in the regular season in his three years on the job. It is somewhat high for a first-time offender — Thornton had never before been fined or suspended — and it seemed clear that Shanahan wanted to send a message in the case. Had the suspension been in the neighborhood of 10 to 12 games, Thornton would likely not have appealed it, according to a source close to the situation.

Thornton will have his appeal heard by NHL commissioner Gary Bettman in a meeting most likely held at the league’s New York offices, where Thornton had his in-person hearing with Shanahan’s player safety team.

Bettman earlier this year upheld a 10-game suspension for Sabres forward Patrick Kaleta, the result of a hit to the head on Columbus defenseman Jack Johnson in October.

Kaleta, a repeat offender, decided to drop his appeal rather than take the next step — an independent arbitrator — as afforded by the new collective bargaining agreement.

Thornton will have the same options. The Bruins forward, represented by the same agent as Kaleta, Anton Thun, could be the first to try the arbitrator. No one has taken that option since the new CBA was put into effect.

The sides have not yet scheduled the appeal with Bettman.

Thornton skated at practice this morning at Ristuccia Arena, the first time he had been with the team since the game against Pittsburgh, but did not speak to the media. He spent the rest of the day in meetings and on phone calls trying to determine whether or not to go ahead with the appeal.

The incident happened at 11:06 of the first period against the Penguins, when Thornton skated over to a scrum during a stoppage in play, knocked Orpik to the ice, and punched him twice. Orpik lost consciousness and was removed from the ice on a stretcher. He was later diagnosed with a concussion and placed on injured reserve, though he resumed light skating Friday.

“This cannot be described as a hockey play that went bad,” Shanahan said in the NHL’s video announcement of the suspension. “Nor do we consider this a spontaneous reaction to an incident that just occurred. Rather, it is our view that this was an act of retribution for an incident that occurred earlier in the game. The result of this action by Thornton was a serious injury to Orpik.”

Thornton’s teammate, Loui Eriksson, was hit on a borderline play by Orpik just 21 seconds into the game. Eriksson was slow to get up and left the game with what was later revealed to be his second concussion in 45 days. He has yet to show any signs of progress.

Thornton attempted to fight Orpik later in the first period, but Orpik declined and Thornton was assessed a roughing penalty.

The 15-game suspension for Thornton means he will forfeit $84,615.45 of his salary, which will go the Players’ Emergency Assistance Fund. If the suspension stands, Thornton would be eligible to return Jan. 11 in San Jose.

He has already missed four games, against Toronto, Calgary, Edmonton, and Vancouver. Thornton is expected to travel and practice with the team while he is suspended.

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